Blood pressure is controlled by both integrated neurogenic and humoral vasoactive mechanisms. 2. Both vasopressor (angiotensin and vasopressin) and vasodepressor (bradykinin) hormonal peptides have been identified. 3. In acute experimental renal hypertension in the rat plasma renin, angiotensin and vasopressin have all been shown to be elevated. 4. Associated with this increase in vasopressor hormonal peptides, urinary kallikrein excretion has been demonstrated to be reduced during the development of renal hypertension. 5. The level of blood pressure achieved in experimental renal hypertension is probably a summation of these vasoactive peptides as well as other factors.